DAVID BASSETT / SCIENCE PHOTO LIBRARY DAVID BASSETT / SCIENCE PHOTO LIBRARY
The heart, a fist-sized, muscular organ, pumps blood through the body, beating about 100,000 times a day. Oxygen-poor blood enters the heart to be pumped into the lungs where it is enriched with oxygen and then is carried back through the heart before it is pumped to the rest of the body. Enhancement of aw403a.
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